Preparation of thiophanthraquinone



Patented Feb. 14, 1950 sf PATENT OFFICE PREPARATION OF THIOPHANTHRA- QUINONE Viktor Weinmayr, Pitman, N. J assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application anuary. 22, 1947, Serial No. 723,664

pound of the formula:

which was first prepared by W. Steinkopi, Ann. 407, 94 (1914) and originally designated by him" as "thiophanthrenequinone. Since the hydro-. carbon compound corresponding to this ketonej was originally named thiophanthracene by Scholl and Seer, Ann. 394, 131 (1912), which nomenclature conforms to that used for compounds of the anthracene series, the term thiophanthraquinone will be employed in the present application to designate the corresponding diketone, in conformity with the nomenclature presently accepted for the corresponding anthraquinone compounds.

According to the literature, the best yield in which thiophanthraquinone was obtained from 2 Claims. (Cl. 260-329) 2 C'. By this method, yields of over 80% of (2- thenoyll-obenzoic acid are obtained. Where the condensation temperature is allowed to drop be-- low-30 C., polymerization of the thiophene be-' comes the predominant reaction, with a corresponding reduction in yield of the desired product. Since thiophene polymerizes rapidly with 8111-: minum chloride even at 0 C., one would expect" that the polymerization would be even more rapid and complete at from 30 to 70 C, for ordinarily the ease with which a compound polymerizes in creases with the temperature. It was therefore surprising that, at temperatures above 30 C., (2- thenoyl) -o-benzoic acid should be obtained in excellent yields. 4 The (2-thenoyl)-o-benzoic acid can be ring-- closed to thlophanthraquinone in yields of better nitrobenzene to temperatures above 90 C.

thiophenewas 11%, the yield of the required These procedures involve a number of unde-f sirable features as far as the commercial produc-- tion of thiophanthraquinone is concerned, such as the poor yields in all steps, the use of a highly i inflammable solvent, the use of readily deliquescent phosphorus pentoxide, or, where sulfuric acid is employed, the ease with which thiophan- --'45 It is therefore an object of this invention to provide a method by which thiophanthraquinona or the intermediate for it, (2-thenoyl) -o-benzoic acid, can readily and economically be made onthaquinone is sulfonated in sulfuric acid.

any desired scale.

I have found that (2-thenoyD-o-benzoic acid can be obtained in excellent yields if the con-" densation of phthalic anhydride and thiophene by means of aluminum chloride is carried out in nil trobenzene at temperatures of between and 70 less otherwise specified.

By combining these two reactions in nitrobenzene as the reaction medium, the process can be carried out which eliminates the necessity of isolating the (Z-thenoyD-o-benzoic acid and"- which gives thiophanthraquinone directly inyields above 66%.

I have also found that the crude thiophanthraquinone can be readily and cheaply purified by dissolving it in sodium sulfide and precipitating it with air.

The process of this invention may therefore be. carried out by condensing phthalic anhydride with thiophene in the presence of aluminum chloride and nitrobenzene at temperatures of from to C., thenadding additional quan titles of aluminum chloride and finishing the con-- densation at from to C., and finallypurifying the crude product with sodium sulfide.

The following examples are given to illustrate. the invention. The parts used are by weight, un-;

- Example! A dry' condensation vessel'of steel or enamel :is' charged with 460 parts of dry nitrobenzene and 208 parts of anhydrous aluminum chloride and 104.! parts of phthalic anhydride are added. The charge is agitated for about one hour to dissolve the aluminum chloride while the temperature rises to 55 C. A solution of 59.4 parts of thiophene in parts of nitrobenzene is allowed to run into the well agitated charge over a period of two hours and at a temperature of from 50 to 55 C. HCl is evolved and slight cooling is required to maintain the reaction temperature at L from 50 to 55 C. The charge is agitated for acid-free.

of from 4. to 6 hours to 120 C.,v and thecharge is.

agitated for about 18 hours while the temperature is held at from 120 to 125 C.

The reaction is then complete, and the reac tion mass appearsas a dark red liquid.

Itis

dropped into a vessel in which 4000parts of cold? water, containing 140 parts of sulfuric acid and 700 parts of ice, are under agitation. Usingmorev or less of the above indicated amount ofyice, the' dilution temperature is allowed to rise to from.

70 to 80 C. After agitating forone hour, the

charge is allowed to separate intoa lower'solvent layer containing the thiophanthraquinone, and

:an upper layer containing the inorganicalue minum salts. This upper layer is drawn off to the sewer, and theisolvent layer is washed -sev-- 'eral times by agitating with water and .separat-z ing as before.

This washing is continued until,

the water-layer reacts only slightly acidg-yor is neutral.

After the last wash, enough caustic is added'to make'the-charge distinctly, alkaline, and.

the nitrobenzene is removed byste-amedistillation. Crude thiophanthraquinone is obtained in theform-of dark colored .needles.

This crude, wet, thiophanthra-quinoneis slurried :in4000 parts of water containing l=par-ts of caustic and 260 parts of 60% sodium sulfide. crystals.- The temperature is raised to.=90 and thegreen-solution is-filtered to removesome insoluble matter. filtrate at from 75 to 90 C- until a. test with lead acetate paper indicates the absence of 'sodi urn sulfide. The thiophanthraquinone--is precipitated as a i'ine, white, crystalline product. It is filtered, washed free of alkali and dried. 100

Air is then blown through the.

parts of thiophanthraquinoneare obtained equal: tea-yield of 66%, based on the thiophene. The product: analyzes 99% pureand melts at from;

The melting point of a repeatedly crystallized.

material was determined as. 230 0.

Example 2 l200.parts of nitrobenzene, 587 parts 'of "amminum chloride and '296 .parts of phthalic 211-, hydride are agitated at from 55 to 6 0 Clfor one hour. The charge is then cooled "to C;

and 168 parts of thiophene are graduallyadded. at a reasonably uniform rate over aperiod off two hours, while. the reaction temperature .is held at from 40 to C." One hour-after-the addition of thiophenelis completed, the-reaction temperature is raised to fror'n.50 to C. and.

held there for about one hour.

The dark red colored reaction 'mass 'is then poured into 11,000 partsofwcold water containing 150 parts of 36% HCl. After agitating for about an hour the nitrobenzene solutionmf the (2-thenoyl) -o-benzoic acid is allowed :to.settle,:.

the. supernatant acid-layer is drawn offand the nitrobenzene layer is washed with cold.zwaten.

until nearly acid-free. The nitrobenzeneis i e-" moved by steam distillation,and-the-('2 -thenoyl-)--.

o-benzoic acid is filtered and washed.:mineraly It is then: heatedto 590 C. -i1'1fi3060 parts of water, and enough-sodium-carbonatedssadded to make-the solution alkaline; The soluetion is "filtered and the-filtrate is slowly "acidiv fied with hydrochloric acid; thereby-precipitate1.-

ing. (2-thenoyl) -o-.benzoic -acid.

3'78 parts of (2-thenoyl)-o-ben'zoic acid are thus obtained, equal to a yield of 81.4% of theory, based on the thiophene employed. This product is pure enough to be ring-closed to thiophanthraquinone without further purification, although it is contaminated with a. small amount of a product formed by the condensation of phthalic anhydride and a polythienyl, which, in contrast to the (Z-thenoyl) -o-benzoic acid, is insoluble when slurried with magnesium carbonate.

Example 3 100 parts of (2'-thenoyl)-o-benzoic acid are added-to a solution of 133 parts of aluminum chloride in 650-parts of nitrobenzene. The temperature is raisedto 120 C. over a period of several hours and held at from 120 to 125 C. -'for -about 18 hours. The resulting dark red solution is poured into water and steam distilled. The-p crudev thiophanthraquinone is filterediroff; Washed.- acid-free :with water, then" washed with :caustic and finally washed free of,- caustic with water. 84.2 parts of thiophanth'raaquinone are obtained, equal to aiyield'of 91.6 based on the (Z-thenoyD-o benzoic acid em"-- ployed.

To purify the productfit is distilled at atmospheric pressure, giving '72 parts of bright yellow thiophanthraquinone melting at 230 0., equal to a yield of 78.1%, based on the (Z-thenoyl) -obenzoic acid employed.

Numerous variations of the above procedure maybe employed. without departing from the 'spirit of the invention. The condensation teme perature of the reaction leading, to the preparation ofthe (Z-"thenoyD -o-benzoic acid mayyary, from 30"to C. Reaction temperatures be-v low- 30 cgdec'rease the yield considerably, and tliepolymeri'z ation of the thiophene becomes. the. predominant, and, in our case undesirable, reac.-. tion. The amount'o'f nitrobenzene can be varied. and is limited only by suchv practical considered tions. as the formation 0f-Itoo -viscous a reactionmass if not enough is. used, or the expenseof recoveringlarge amounts of solvent-if too much is used. The amount of nitrobenzeneused in two .parts-in the first example may "all be used fromthe start. Howeven-theuse from thestartv of. all the aluminum chloride neededin the firstexample tends -=tolower the yieldfor thiophanth'raquinone- I-tis desirable that the thiophene be added insmall amounts to the aluminum" chloride iphthalicanhydride solutionras the reaction pro-: ceeds, so,that noappreciable amount of theuncondensed thiophene -is in contact with the aluminum chloride for any extended period of time. The zcondensation. of the thiophene. with thegphthalic .anhydride proceeds -.-very rapidly, and;

further heating after-the addition of all offthe-athiophene is: notusually :required;

The wing-closure of the (Z-thenoylt-b-benzoic acidto--the thiophanthraquinone takes place at? temperatures above= C. The time: chosen-tor 'reachingthat temperature, hasrlittle significance uponithe yield. Thetime of heating to temperaturesof from -to C. may alsoxvary'over a =wide range. Ring-,closurehas taken-place to a' large extent after two hours ofjhe'ati'ng and is-zessentially complete after? 18 :hours. This 'time may be shortened byraising the temperature 1 above 1.30 C'.,- such as to C., and willib'e cor.- respondinglyprolonged-i at temperatures below 1 120? C.. 1. While temperatures of upio 180?; icsmay be employed, such higher temperatures ofier no particular advantages.

The crude thiophanthraquinone may be purified by methods used for the purification of the related anthraquinone, such as extraction with alkaline hydrosulfite, extraction with solvents, crystallization from sulfuric acid of a suitable concentration, sublimation or distillation. However, the purification with sodium sulfide, which is not applicable to anthraquinone, is particularly suitable in this process as it can be accomplished at a low cost.

The condensation of the phthalic anhydride and thiophene to produce the (2-thenoyl)-obenzoic acid is brought about by the use of substantially the theoretical amount of aluminum chloride required to efiect such a condensation, namely, two mols of A1013 per mol of phthalic anhydride. Excesses of from to 25% are usually employed to ensure complete reaction, for in many cases the aluminum chloride is not pure. Large excesses, while operable, are not essential and merely add to the cost of the process. The ring-closure of the (2-thenoyD-obenzoic acid is also preferably carried out with approximately two m'ols of aluminum chloride (AlCla), again sufficient excesses being employed to ensure complete reaction, as in the case of the condensation reaction above mentioned. Again, large excesses of the aluminum chloride in the ring-closure are not required.

It is obvious from the foregoing that the preparation of thiophanthraquinone in a good yield does not have to be carried out in one step, and that the (2-thenoy1) -o-benzoic acid may first be isolated and then ring-closed. This process provides not only a method of producing thiophanthraquinone in a gOOd yield, but also provides a method for the preparation of (2-thenoyl) -o-benzoic acid in a good yield.

This method is not limited to thiophene alone, but can be used with substituted thiophenes such as 2-chlorothiophene, Z-methylthiophene or 3- methylthiophene, as disclosed in pending applications Serial Nos. 723,6-67, 723,668, and 723,669, filed simultaneously herewith.

The process of condensing phthalic anhydride with thiophene in nitrobenzene with aluminum chloride at temperatures of from 30 to C. gives (2-thenoy1) -o-benzoic acid in a good yield. The ring-closure of (2-thenoyl)-o-benzoic acid in nitrobenzene by heating at from to 150 C. also gives good yields of the thiophanthraquinone, and the combination of these two procedures into one process eliminates the necessity of isolating the (2-thenoyl) -o-benzoic acid. The process also provides a novel and efiective method of purifying the crude thiophanthraquinone.

I claim:

1. A process for preparing thiophanthraquinone which comprises heating phthalic anhydride and thiophene in nitrobenzene and in the presence of aluminum chloride at temperatures of from 30 to 70 C., continuing the heating until the condensation is essentially complete as evidenced by substantial cessation of the evolution of hydrochloric acid gas, and efiecting ringclosure of the resulting (2-thenoyl) -o-benzoic acid without isolation from the nitrobenzene by heating in the presence of aluminum chloride at temperatures of from to C.

2. An improvement in the process of preparing (2-thenoyl)-o-benzoic acid which comprises heating phthalic anhydride and thiophene in nitrobenzene and in the presence of aluminum chloride at temperatures of from 30 to 70 C. and continuing the heating until the condensation is essentially complete as evidenced by substantial cessation of the evolution of hydrochloric acid gas.

VIKTOR WEINMAYR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,826,621 Lloyd Oct. 6, 1931 1,856,231 Stowell May 3, 1932 OTHER REFERENCES Thomas, Anhydrous Aluminum Chloride,"

pages 523, 540, 541, Reinhold Pub. 00., 1941.

Galloway, Chemical Reviews, vol. 17, pages 372, 374 (1935). 

1. A PROCESS FOR PREPARING THIOPHANTHRAQUINONE WHICH COMPRISES HEATING PHTHALIC ANHYDRIDE AND THIOPHENE IN NITROBENZENE AND IN THE PRESENCE OF ALUMINUM CHLORIDE AT TEMPERATURES OF FROM 30* TO 70*C., CONTINUING THE HEATING UNTIL THE CONDENSATION IS ESSENTIALLY COMPLETE AS EVIDENCED BY SUBSTANTIAL CESSATION OF THE EVOLUTION OF HYDROCHLORIC ACID GAS, AND EFFECTING RINGCLOSURE OF THE RESULTING (2-THENOYL)-O-BENZOIC ACID WITHOUT ISOLATION FROM THE NITROBENZENE BY HEATING IN THE PRESENCE OF ALUMINUM CHLORIDE AT TEMPERATURES OF FROM 120* TO 125*C. 